1.4 Model Outline

Figures A, and B (on the following pages) outline
the conceptual framework and the main inputs of the model. These are described
in more detail in Section 2.2 of the manual.

Figure A outlines the inputs used to describe how the
patterns of HIV collection and testing that occur within a particular setting,
how this has changed as a result of the intervention, and how this may influence
the prevalence of HIV infection among blood transfused. In the figure, text
written in italics represents inputs required by Blood 3.0. Text that is
not in italics represents information that is calculated from these inputs. For
example, the number of units of blood available for transfusion in any year will
be dependent upon the total number of units collected; the proportion of blood
collected from low risk compared with random donors; the percentage of each that
is HIV tested; and the percentage of blood tested that tests HIV negative, and
does not test positive for other diseases (such as syphilis or hepatitis).

Figure B outlines the inputs used to estimate the numbers
of HIV infections averted among the main groups receiving blood products, and
surviving to discharge. Again, text written in italics represents inputs
required by Blood 3.0. Text that is not in italics represents information
that is calculated from these inputs. Estimates of the prevalence of HIV
infection in blood transfused, HIV prevalence among the main recipient groups,
and estimates of the distribution of numbers of units provided to the different
recipient groups are used to estimate the numbers receiving blood products, and
the numbers of HIV infections that may occur. Comparisons between the estimates
made in the presence and absence of the intervention are used to estimate the
total number of HIV infections averted from the provision of safe blood
products. This is combined with inputs describing the percentage of individuals
within the main recipient groups surviving to discharge to obtain the final
estimates of the total number of HIV infections averted by the intervention.